CORRESPONDENCE_2008 (1/08 TO 6/08)

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11 THOMAS R. FLINN DIRECTOR January 28, 2008 Mr. Todd Del Frate California Regional Water Quality Control Board 11020 Sun Center Drive, #200 Rancho Cordova, California 95670-6114 Ll P. 0. SOX 1810 -1510 E. HAZELTON AVENUE STOCKTON, CALIFORNIA 95201 (209) 468-3000 FAX (209) 468-2999 www.sjgov.org SUBJECT: CONCEPTUAL CLOSURE DESIGN, CORRAL HOLLOW SANITARY LANDFILL Dear Mr. Del Frate: Attached, please find figures showing the design concept for the extension of the closure cap at the Corral Hollow Landfill (Figures 1-4). This letter addresses the two core design aspects of that work. Closure Cover Extension Area We propose to extend the closure cover over all refuse within our property, including the burn ash found along our eastern perimeter based on our recent investigation and in accordance with the request from Robert McClellon of San Joaquin Environmental Health Department (Figure 2). We appreciate the assistance by Mr. McClellon's staff with this investigation. This closure area also reflects the directives received in our meeting on January 7, 2007 with Water Quality Control Board, Integrated Waste Board, Cal Trans, and Environmental Health Department staff. In that meeting, it was decided that the closure cap extension within our property could proceed as a separate project. Extending the closure cap to cover all refuse in a single project would be ideal, but such a project requires participation by CalTrans, and CalTrans has so far indicated reluctance to participate. Rather than delaying the project until CalTrans participation is assured, we will proceed independently on our own property. Closure Method The second important design feature is the use of Geocomplsite Clay Liner (GCL) as an engineered alternative to the low -hydraulic -conductivity layer in accordance with Title 27 Section 21090 (Figure 3). According to our design consultant, GCL has been successfully used as closure cap at the Cold Canyon Landfill in San Luis Obispo and the Morongo Landfill, San Bernardino, CA. I am personally aware of closure with GCL at the Contra Costa Sanitary Landfill near Antioch, CA. It is also my understanding that Water Board staff considers GCL superior to the prescriptive one -foot clay layer barriers due to GCL's resistance to cracking. Important features of this method include: • Extension of the closure cap two feet into CalTrans property. CalTrans has previously expressed a desire to cooperate by allowing access to their property.