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adequately address the performance of single composite liners in either WMU D-02 or the <br /> expansion areas. Staff requested additional information and expects to resolve the liner question <br /> for the expansion area in the future. <br /> Forward Inc. states that the existing area D waste units will run out of capacity in July and in <br /> order to timely complete a new unit construction must start in April. They request that staff <br /> consider approval of construction of a single composite liner for the final waste management unit <br /> in currently permitted area D. <br /> Construction of Class II waste management units within area D has been previously permitted <br /> under the provisions of Waste Discharge Requirements (WDRs) Order No. 97-141. These <br /> WDRs specifically permit construction of a single composite liner for Class II waste <br /> management units within the approximately 100 acres of area D. Forward Inc. has been <br /> constructing Class H units within area D with a single composite liners since 1993 and in that <br /> time period has developed a track record of high quality construction and good operational <br /> practices. There is no evidence of a release of contaminants to the environment from the single <br /> composite lined units at Forward Landfill. <br /> Other site-specific reasons regarding why a single composite liner is appropriate for the final D <br /> area waste management unit include: <br /> 1. There are approximately forty-five (45) feet of separation between the bottom of the <br /> waste unit and groundwater. Native soils at the site are composed of intercalated clay, <br /> silt, and sand and have generally low hydraulic conductivity. <br /> 2. Forward proposes to construct the unit with a double composite liner under the sump <br /> area. <br /> 3. Forward has committed to aggressively control landfill gas and is completing plans for <br /> installation of gas control facilities. <br /> 4. This is the final 10-acre parcel in a previously constructed 100-acre landfill area <br /> composed of multiple, single composite lined waste units. Construction of a double <br /> composite liner at this time in the final comer parcel will present unique and difficult <br /> constructability problems. Constructability problems that will have to be resolved <br /> include: matching a double liner with two existing single liners; continuity of leachate <br /> drainage pipes; and stability issues resulting from multiple geomembrane layers (which <br /> can act as failure plains) in an area exposed to lateral stresses from two directions. <br /> Discussion <br /> Staff supports approving the completion of area D with the liner system described in WDRs <br /> Order No. 97-141. The primary reasons are WMUD-02 is the last 10-acre parcel in a previously <br /> constructed 100-acre landfill, and connecting a double composite liner system with two existing <br /> single liner systems would be technically difficult and may cause stability problems that could <br /> compromise the liner system. Staff also supports the completion of area D because Forward Inc. <br /> has had an excellent construction and QA/QC track record when installing their liner, the <br /> monitoring data from the lined portion of the landfill has not shown a release, and this landfill <br /> will run out of capacity in July 2002. However, this resolution does not preclude staff from <br />