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' Environmental Consultants 4707 Greenleaf Circle 209 545-8490 Suite F Fax 209 545-8391 Modesto, CA 95356 www.scsengineers.com November 27, 2006 File No. 07206050.00 Task 1 Mr. Dan Johnson County of San Joaquin Post Office Box 1810 Stockton, California 95201 Subject: San Joaquin Valley Air Pollution Control District(SJVAPCD)Rule 4642 Surface Emissions Testing at the Corral Hollow Landfill, Tracy, California Dear Mr. Johnson: This letter provides results of the October 20, 2006, SJVAPCD Rule 4642 landfill emissions monitoring performed by SCS Field Services (SCS) at the subject site. All work was performed in accordance with our County approved Work Scope (Task 1) contained in our proposal dated October 24, 2006. Summary and Conclusions - -- - -- --- -On October 20, 2006, surface emissions testing showed no exceedences of the SJVAPCD Rule 4642 threshold limit of 1,000 parts per million by volume (ppmv). As stipulated in SJVAPCD Rule 4642 upon completion of two successive semi-annual tests without an exceedence of the 1,000 ppmv standard, other than non-repeatable momentary readings, the testing frequency may be decreased to once every calendar year. Based on these test results with no exceedence of 1,000 ppmv, no additional testing is required for a period of one year. Therefore, the next surface test event is due by the Month of November 2007. Background As you know, the Corral Hollow site is a close former organic refuse disposal site. By way of background, organic materials buried in a landfill decompose anaerobically (in the absence of oxygen) producing a combustible gas, which contains approximately 50 to 60 percent methane gas, 40 to 50 percent carbon dioxide, and trace amount of various other gases, some of which are odorous. The Corral Hollow property contains a LFG collection and flare system to control the combustible gases generated in the landfill. The gases produced in a landfill will either vent vertically to the atmosphere or migrate horizontally through subsurface soil to locations on adjacent properties. If the soil surrounding a landfill consists of permeable materials, there is a greater likelihood that the LFG will migrate to off-site locations. If the methane gas component of LFG is allowed to accumulate in a confined area (i.e., utility lines, irrigation valve boxes, vaults, basements, wall spaces, etc.) and is exposed to an ignition source, it can be explosive at concentrations between 5 and 15 percent by volume. Offices Nationwide