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THOMAS R. FLINN DIRECTOR Mr. Robert McClellon, REHS Environmental Health Department 600 East Main Street Stockton, California 95202 May 14, 2008 n R. O. BOX 1810.1810 E. HAZELTON AVENUE STOCKTON, CALIFORNIA 95201 (209) 468-3000 FAX (209) 468.2999 www.sjgov.org1pubworks SUBJECT: DESIGN OF LANDFILL GAS PERIMETER MIGRATION WELLS AT THE NORTH COUNTY AND FOOTHILL SANITARY LANDFILLS Dear Mr. McClellon: As promised, attached are drawings showing the design of the landfill gas (LFG) perimeter migration monitoring wells at the North County Recycling Center and Sanitary Landfill and Foothill Sanitary Landfill. These wells will be installed in compliance with recently -enacted Section 20925 of the California Code of Regulations (CCR) Title 27. Our recent conversations raised two issues addressed in this letter: well depth and construction of the probes within the wells. The well depths are selected based on the final maximum depth of the refuse at each landfill. This allows us to install all proposed wells at the Foothill Landfill and meet the intent and spirit of Section 20925. Note that six wells in the southeast corner of the Foothill site would be less than 10 feet deep if the present refuse base elevation was used as criterion for the depth of the well. These shallow depths result from a 70 -foot decrease in ground elevation from the west side of Module "I" (elevation 300) to the southeast portion of our property (elevation 230). Installing wells to a depth of 10 feet based on the existing refuse elevation would be impractical, and we request that we use the future refuse base elevation for our design criterion. Such adjustments are allowed by Section 20925(c)(2) in cases of impracticality. It seems clear that wells at the proposed depths would be "sufficient to detect migrating landfill gas and provide protection to public health and safety and the environment", per the referenced Section. However, if you or Waste Board staff believe that these wells should not be installed until the final refuse depth is reached (decades from now), then we can postpone the installation of those wells until that time. You asked for clarification of the location of the probes within the wells, particularly regarding the depth of the deep probe. Each probe (perforated portion of the sampling pipe) extends nearly the full length of its rock -filled sampling section, from the bottom to within 18" of the top of that section (see notation to the well drawing to identify the probe on attached figures). Title 27 Section 20925 paragraph (c)(1)(C) states that the "probe" should be placed "at or near the depth of the waste". A probe extending the full length of the rock section would comply with this provision because a portion of the probe is at the elevation of the base of the waste. It seems that this is the best possible way to comply with that provision.