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I ,e I 'W a 0 .2al 4 California Regional Water Quality Control Board Valley Region Robert Schneider,Chair 9Central Winston H.Hickox Gray Davis Secretary for Sacramento Main Office Governor Envirownental Internet Address: http://www.swrcb.ca.gov/rwqcb5 Protection 3443 Routier Road,Suite A,Sacramento,California 95827-3003 Phone(916)255-3000-FAX(916)255-3015 Ho 14 August 2002 AUG 15 2002 Mr. Kevin Basso ENVIRONMENT HEALTH General Manager PERMIT/SERVICES Forward Inc. PO Box 6336 Stockton, CA 95206 LINER PERFORMANCE APPRAISAL—PERFORMANCE DEMONSTRA TIONFOR A SINGLE COMPOSITE LINER, FORWARD AND AUSTIN ROAD LANDFILLS, SAN JOAQUIN COUNTY (Case No. 2209 & 2148) On 26 March 2001 Central Valley Regional Water Quality Control Board staff(staff)requested that Forward Inc. provide a demonstration that any future waste containment units fulfill the performance standards for a Class II landfill. On 21 February 2002 Forward Inc. submitted "Leachate Attenuation Analyses Prescriptive Clay Liner, Forward Landfill"and on 21 March 2002 staff provided comments for that document. On 10 July 2002 Forward provided the Performance Demonstration for a Single Composite Liner that responded to those comments. Staff's comments on the liner performance demonstration are as follows: 1. The new document includes a revised Leachate Attenuation Analyses Prescriptive Clay Liner as an Appendix to the demonstration. This appendix models natural attenuation of VOCs as leachate passes through the compacted clay liner(CCL). The models used, BIOCHLOR and BIOSCREEN, simulate the reduction of VOC concentrations by the processes of dispersion, sorption, and biodegradation. Model inputs include flow rates, chemical retardation factors, and published natural attenuation rates. The model projects greatly reduced VOC concentrations in leachate when it exits the CCL. Staff remains skeptical that two feet of clay contain sufficient nutrients and substrate to support the levels of biodegradation projected by the model. Additionally, the small amount of clay in a two feet thick CCL may have insufficient sorption capacity. We believe that although the CCL is engineered to achieve a very low hydraulic conductivity and thus a long residence time, the mass of clay contained within the two feet thick CCL is very small and will be the limiting factor that determines how much attenuation can occur. If peer reviewed research that we are not aware of, supports VOC attenuation in similar compacted clay, we would reconsider this aspect of your demonstration. Without supporting documentation, staff must conservatively assume that chemical concentrations in leachate that exits the CCL will be similar to initial concentrations. Please revise Appendix A to include average (over the last 5 years) Forward landfill leachate unaffected by attenuation to calculate concentrations released at the base of the liner and to model the expected impacts to groundwater. Staff will make decisions based on this worse case assumption; any leachate California Environmental Protection Agency_ Q*Recycled Paper The energy challenge facing California is real. Every Californian needs to take immediate action to reduce energy consumption. For a list of simple ways you can reduce demand and cut your energy costs,see our Web-site at http://www.swreb.ca.gov/rwqcb5