Laserfiche WebLink
Alternative final cover systems are allowed if their performance is equivalent or superior <br /> to the prescriptive cover design. Alternative final cover systems are becoming a <br /> commonly accepted design for final closure of municipal solid waste facilities in <br /> California. Alternative final cover systems combine the effects of a soil with moderate <br /> hydraulic conductivity and an established plant community to provide infiltration control <br /> through evapotranspiration(ET).. <br /> The alternative final cover system at the FSL was constructed using 4-feet of select on- <br /> site borrow soils as described in the"Construction Quality Assurance (CQA) Report: <br /> Stage 1A Partial Final Closure at the Forward Landfill' (Vector Engineering, Inc., <br /> 2006). While the initial performance of these soils satisfied the minimum performance. <br /> criteria for a prescriptive final cover constructed over an unlined waste footprint,FSL <br /> elected to monitor the performance of this as-built.prescriptive system for two reasons. <br /> First, it is understood that the performance characteristics of a prescriptive final cover <br /> over an unlined footprint are likely to degrade over time. As a result, it is anticipated that <br /> within a relatively few years the initial prescriptive performance will degrade. As a <br /> result,FSL considered it more practical to install the final cover as a prescriptive system <br /> but maintain it as an alternative. This allowed for the establishment of more robust and <br /> deeper rooting plant communities that will be more effective at controlling infiltration <br /> over the long term. The second purpose of the monitoring was to establish a performance <br /> history that would allow FSL to seek regulatory approval of this final cover section as an <br /> alternative to the prescriptive final cover over lined portions of the site. <br /> Subsequent to final cover construction, GLA installed moisture monitoring probes and <br /> lysimeters at site (Figures 1 and 2)and began monitoring the final cover on July 28, <br /> 2006. <br /> 1.2 MONITORING SYSTEM INSTALLATION <br /> On July 24, 2006 after notifying the RWQCB and the LEA, GeoLogic Associates (GLA) <br /> began installation of the moisture monitoring equipment at the locations shown in Figure <br /> 1. In addition,heat dissipation sensors (HDU 229-L)from Campbell Scientific Inc., soil <br /> moisture probes from Echo Sensors, and Gee Passive Capillary Lysimeters manufactured <br /> by Decagon Devices, Inc.,were installed at each of the two monitoring locations. Figure <br /> 2 illustrates the configuration of the instruments installed at each monitoring location. <br /> The Gee Passive Capillary Lysimeters were installed at the base of the cover system in <br /> order to evaluate moisture migration through the bottom of the cover. During installation <br /> of these devices, refuse encountered below the 48-inch thick alternative final cover <br /> section was placed in bags and/or was removed with a loader to the existing active refuse <br /> disposal area. In addition to the lysimeters, soil moisture monitoring instruments and <br /> heat dissipation units were installed at 12", 24"and 36"depths below the ground as <br /> shown on Figure 2. Backfill of the excavations required for instrument installation <br /> incorporated the soils that were generated from the initial excavations. Backfilling and <br /> compaction was accomplished using a loader and manual tamper and compaction of the <br /> backfill was monitored using a nuclear density device (Troxler Electronics Lab. Inc., <br /> 2 <br /> GeoLogic Associates <br />