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of several factors in its computation; soil infiltration, vegetative cover, relief of slopes and surface storage. The rainfall intensity is based on a duration equal to the time of concentration. The time of concentration is defined as the time required for water to flow from the hydraulically most distant point in the watershed to the point of design. The drainage plan for the final grading plan is shown in Drawing 9. The drainage network for the completed landfill is designed to intercept and convey flows from a 24-hour, 1,000-year storm event and to protect the landfill from erosion. The preliminary design criteria for the stormwater sedimentation basins are listed below: • North Area surface water sedimentation basin volume 38 acre-feet • South Area surface water sedimentation basin volume 12 acre-feet • West Area surface water sedimentation basin volume 30 acre-feet • Maximum basin side slope 3:1 (H:V) • Minimum basin base slope 3 percent The sedimentation basins have adequate storage volumes to hold potential silt generated from the landfill based on the USLE analysis (see Appendix 1). 5.3.7 LANDFILL GAS GENERATION AND AIR EMISSIONS CALCULATIONS in accordance with the S)VAPCD regulations, a landfill gas control/recovery system has been designed for the future Forward Landfill. Calculations regarding estimated gas generation and air emissions were conducted to properly design the gas control system. These calculations were made to provide for the construction of an efficient LFGES. The proposed LFGES will be expanded accordingly as the landfill develops. Estimates of the landfill gas generated in each of the current (year 2000) in-place refuse prisms were added to the estimate of the landfill gas generation from the future combined fill areas. The landfill gas generation rate estimates were determined using the US EPA "Landfill Gas Emissions Model Version 2.0" (LandGEM) and EPA "Compilation of Air Pollution Emission Factors (AP-42)". In accordance with AP-42 ("Compilation of Air Pollutant Emission Factors", 5"' Ed., EPA, 1997), a default k of 0.02/yr (the methane generation rate constant) is ronvard Landfill JTD 5-25 L\Allied\2000.193\Reports\JTD-PC PCMP702:Sec•5.0:5/24/02 Revision 1:07/16/02 BRYAN A.STIRRAT 6 ASSOCIATES