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required in California,this final cover must, at a minimum, include a foundation layer, a low-permeability barrier layer, and a top soil vegetative layer that will be able to support erosion-limiting vegetation. Current minimum standards for the low permeability barrier layer are: • A maximum saturated hydraulic conductivity of 1x10-5 cm/sec on an unlined site in most areas outside of California(40 CFR part 257 &258 "Subtitle D"), • A maximum saturated hydraulic conductivity of 1x10-6 cm/sec for an unlined site in California(CCR Title 27), • Or a saturated hydraulic conductivity equal to or exceeding that of the bottom liner on a lined landfill (Subtitle D and CCR Title 27). Whereas the intent of the federal and state prescribed cover system is to protect the environment by providing a minimum design criteria, it is recognized that the prescribed system may not be the most environmentally sound or cost-effective system in every climatic setting. In recognition of the possibility that an alternative system may perform more effectively in local environments, the regulation for landfill final closure allow for engineered alternatives to the prescribed standard. The use of an alternative final cover system is expected to minimize problems caused by desiccation and settling induced cracking, enhance vegetation survival and facilitate post-closure maintenance. TECHNICAL APPROACH California is an"approved State"under Subtitle D, so the CWRCB, RWQCB, LEA, and CIWMB may authorize the use of an alternative landfill final cover system if equivalent engineering performance can be demonstrated. To this end, it is the intent of AWI, to demonstrate that an alternative final cover at the Forward Landfill can effectively minimize percolation of surface water through the cover and into the waste prism. GLA's technical approach to instrument the final cover for moisture monitoring at the Forward Landfill will include the following components:. Task 1 - Moisture Monitoring The Forward Landfill (FL) final cover project relies to a large extent on monitoring of system performance through accurate measurements of moisture movement within the cover system. The soil moisture monitoring system proposed for the FSL is composed of soil moisture probes, data recording equipment and software for downloading data. The moisture sensors will be wired to a centrally located data recorder(multiplexer) to minimize cable length and the data recording equipment will measure and convert the analog sensor values into a digital data record that will store these data values in non- volatile memory. The soil moisture stacks will consist of 8 water content reflectometers placed at different depths in the cover profile to provide an uninterrupted vertical profile of soil moisture for the 4-foot thick final cover. The soil moisture monitoring probe "stacks" and data recording equipment will be housed in an enclosure to minimize C:\2005-0082\workplan.DOC\07/11/05 —2— GeoLogic Associates