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As-Built CQA Report for the Construction of Area 2A at the Foothill Sanitary Landfill San Joaquin County,California 3.0 SOIL GAS COLLECTION PIPE AND LYSIMETER 3.1 GENERAL A soil gas collection pipe and a lysimeter were constructed below the grade of the Area 2A composite liner system. These features,installed to provide a means to control gas and monitor the vadose zone, included geomembrane, geotextile, gravels, Controlled-Low Strength Material (CLSM), and piping required for monitoring and testing in accordance with the CQA Manual. 3.2 SOIL GAS COLLECTION PIPE The Soil Gas Collection Pipe system beneath the floor of Area 2A included a trench consisting of perforated 4-inch HDPE pipe (SDR 11) surrounded by GDM and encased by 8-oz non-woven filter geotextile. The soil gas system details are shown on Sheets C-2 and C-6 of the Construction Drawings, which are included in Appendix D.1. The perforated soil gas collection pipe and gravel section was terminated at the toe of the eastern slope. A solid riser pipe was extended from the termination of the perforated section to a surface completion at the top of the eastern slope. The trench with the solid riser pipe section was backfilled with CLSM,a mixture of sand and cement. A CAT 320 excavator was used to excavate the soil gas trench across the floor and up the eastern slope. The excavation was performed through placed foundation layer soil. The excavation on the floor was staged to separate the upper 1 foot of foundation layer soil from underlying native materials. Along the floor, laborers installed 8-oz geotextile and fusion welded perforated HDPE pipe. A CAT 430 backhoe was used to haul and place GDM around the perforated pipe up to the grade of the base of the foundation layer soil. The excavated foundation layer soils were moisture conditioned and used to backfill and compact the upper portion of the trench using a vibratory plate compactor. Laborers also installed and fusion welded the solid riser section up the eastern slope. The riser trench was backfilled with 16 cubic yards of CLSM to complete the installation. The CQA activities during installation of the soil gas collection pipe included: ■ Review of MQC data and conformance tests of 8-oz geotextile. ■ Sampling and gradation testing of LCRS granular drainage material. ■ Observation of fusion welding of perforated and solid sections of HDPE pipe. ■ Observation during trenching and placement of geotextile, piping and GDM in perforated sections. ■ In-place density testing of foundation layer soil backfilled over the soil gas collection pipe on the floor. PA14 Projects114-101(SJCDPW North County and Foothill)IFoothill CQA1Report\Final ReportToothill CQA Rport-Final.docx P011