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f Califor ' Regional Water Quality C rol Board ;...r <br /> e :. <br /> Central Valley Region r <br /> Katherine Hart,Chair <br /> N <br /> 11020 Sun Center Drive,#200,Rancho Cordova,California 95670-6114 <br /> Matthew Rodriquez, (916)464-3291 -FAX(916)464-4645 Edmund G.Brown Jr. <br /> Secretaryfor http://www.waterboards.ca.gov/centralvalley Governor <br /> Environmental Protection <br /> RECB�J - <br /> 13 December 2011 17- <br /> DEL' <br /> DEL' 2011 <br /> W. Michael Carroll Dennis Agar <br /> Solid Waste Division Deputy District If, �, 3 <br /> San Joaquin County Dept. of Public Works California Department of Transportation <br /> P.O. Box 1810 P.O. Box 2048 <br /> Stockton, CA 95201 Stockton, CA 95201 <br /> REQUEST FOR ADDITIONAL INFORMATION ON USE OF GEOSYNTHETIC CLAY LINER <br /> (GCL) AS LANDFILL COVER; WASTE DISCHARGE REQUIREMENTS ORDER R5-2001- <br /> 176 (WDR ORDER); SAN JOAQUIN COUNTY DEPARTMENT OF PUBLIC WORKS <br /> (DISCHARGER); CORRAL HOLLOW SANITARY LANDFILL (CHSL); SAN JOAQUIN <br /> COUNTY (COUNTY) <br /> Central Valley Water Board staff ("Board Staff') has investigated the use of GCL alone as an <br /> alternative replacement for Title 27 Section 21090 (a)(2) Low-Hydraulic-Conductivity Layer <br /> prescriptive requirement of one foot of soil compacted to attain an hydraulic conductivity of <br /> 1x10-6 cm/sec (i.e., 1 ft/yr) or less. <br /> Board Staff is concerned that the use of GCL without an adequate thickness of cover soil <br /> above the GCL to provide sufficient confining stress within the GCL will not be equivalent to <br /> one foot of soil that does not significantly desiccate with a maximum hydraulic conductivity <br /> requirement of 1x10-6 cm/sec . <br /> Attached is an email conversation (See Enclosure 1) with GSE, a major manufacturer of GCL <br /> products. The concern is that the proposed design of two (2) feet of cover soil will not provide <br /> enough confining stress within the GCL material for the GCL to meet its advertised maximum <br /> permeability of 5x10-9 cm/sec as tested per ASTM 5084. The ASTM 5084 test applies 5 psi <br /> maximum effective confining stress and 2 psi head. These conditions are far different from the <br /> proposed design at CHSL. The manufacturer acknowledges that hydraulic conductivity <br /> increases as confining stress within the GCL decreases. Board Staff requests that the design <br /> engineer provide supporting information that the proposed design of two feet of cover soil over <br /> the GCL meets or exceeds Title 27 requirements for maximum hydraulic conductivity. <br /> We also are concerned that the GCL will not meet the performance standards of Title 27 with <br /> the seasonal wetting and drying of the cover. As the GCL dries out it will desiccate causing <br /> very high conductivity until the GCL is once again fully hydrated. Also, Board Staff is unsure <br /> California Environmental Protection Agency <br /> C, Recycled Parer <br />