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FORWARD LANDFILL LEACHATE VOLUME GENERATION NARRATIVE The following information and assumptions were utilized to develop leachate generation volumes: A. REFERENCES/MATERIAL REVIEWED 1. Annual leachate totals for the Forward Landfill 1991 through 2001. 2. Annual rainfall (precipitation) totals - Stockton Airport Weather Station - 1991 through 2001. 3. WMU FU-North leachate impoundment basin information from "Design and Construction Documents for WMU-D-99, Class II Leachate Impoundment and Closure of Eastern Ash Pit WMU Interim F, Forward, Inc. Landfill (CH2M Hill, April 1999) Appendix F including Pan Evaporation Values for the Site. B. ASSUMPTIONS 1. Leachate production within the Austin Road area will approximate leachate production data as recorded at the Forward Landfill on a per-acre basis. 2. Operation activities including thickness of waste for initial areas, diversion of flow away from cells and leachate production minimization practices for the balance of the site will be similar to those activities practiced during the 12- year leachate production record collection period. 3. Conservative values for evaporation volumes based on smallest basin surface area (bottom of Basin WMU F-West) were used. 4. Maximum values for precipitation based on largest basin surface area were used. 5. Leachate production for the Forward Landfill diminished during 2000 and 2001, even though average annual rainfall was approximately equal to the 12-year average. The trend (lower leachate production rates) should continue as operations at the Forward site decline. The 2000 and 2001 average value was used for WMU F-North leachate generation rate. 6. Both the existing WMU F-North and the WMU F-West leachate surface impoundment will be utilized to manage the overall Forward Landfill leachate disposal. 1 BRYAN A. STIRRAT AND ASSOCIATES L:\Allied\Forward Landfill\FU-03 Basin\Design Rpt-LE\LEACHATE VOLUME 081603.Doc