CORRESPONDENCE_2007 (1/07 - 6/07)

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i A u, :< THOMAS R.FLINN P.O.BOX 1810-1810 E.MAZELTON AVENUE DIRECTOR STOCKTON,CALIFORNIA 95291 ; daw (209)468-3000 FAX(209)468-2999 1 wrww.sjgov,orglpubworks THOMAS M.GAU9 CHIEF DEPUTY DIRECTOR MANUELSOLORIO Worldng for YOU DEPUTY DIRECTOR STEVEN WINKLER DEPUTY DIRECTOR ROGER JAMES January 12 2007 BUSINESS ADMINISTRATOR "� Mr. Robert McClellon, RENS Environmental Health Department 304 East Weber Avenue, Third Floor Stockton, California 95202 SUBJECT: PHASE 2 WORKPLAN TO ASSESS EXTENT OF CLOSURE CAP AT THE CLOSED CORRAL HOLLOW LANDFILL Dear Mr. McClellon: Enclosed, please find the Workplan for the Phase 2 Investigation of the Extent of the Closure Cap(with Health and Safety Plan) at the Corral Hollow Sanitary Landfill, revised per your comments, those of Gino Yetka of the California Integrated Waste Management Board, and those received from Regional Water Quality Control Board staff. These revisions include additional investigations north and west of the Phase 1 area, and south and west in the general vicinity of the retention pond. Earlier findings that the refuse did not extend east of the access road will be verified. All work will be done in accordance with the Health and Safety Plan approved by Environmental Health Department. We do not intend to remove any refuse in this investigation. Previous submittals presented the likely method of extending the closure cap, where needed, using Geocomposite Clay Liner(GCL). This continues to be the most likely method where appropriate; however, Water Board staff has recently required that the County evaluate means to reduce or eliminate the volatile organic compounds (VOCs)detected at shallow aquifer monitoring well MW-5. This well is north of monitoring well SB-1, downgradient from a portion of the area where the closure cap would be extended. We contemplate coordinating the extension of the closure cap with enhancement of landfill gas (LFG) collection in that area. This enhancement in that area may include the extension of the closure cap using a plastic membrane, rather than GCL, and installing a shallow horizontal LFG collection trench beneath the membrane. Normally we would not propose overlaying refuse with impermeable plastic because such membranes obstruct the venting of LFG. In this case, no new refuse will be placed over the membrane (if this method is selected), so we will be able to monitor the effectiveness of the collector, and make adjustments as needed. Such design decisions will be finalized after this Phase 2 work and other work required by Water Board staff. We will keep you informed of our discussions with Water Board staff.