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S <br /> r M11 JJW GEOSCIENCES Inc. General Engineering Contractor(CA Lic#706568) <br /> CA DHS Certified Analytical Laboratory(ELAP#2012) <br /> Environmental Consultants well Drilling Contractor(C-57 License#706568) <br /> &a Engineering Contractor OSHA Certified Asbestos Consultant(#92-0814) <br /> March 9, 1999 <br /> Mr. Bill Hunter <br /> William J. Hunter &Associates <br /> 2220 Loma Vista Drive <br /> Sacramento, CA 95825 <br /> Subject: California Welding Supply Company <br /> 1000 E. 11 th Street <br /> Tracy, California <br /> San Joaquin County Site Code: 2083 <br /> EXPLANATION OF MASS BALANCE CALCULATIONS <br /> Dear Mr. Hunter: <br /> Per your request, this letter is to provide additional explanation of the mass balance calculations <br /> computed for the above-referenced site. JJW Geosciences, Inc. performed the initial mass balance <br /> calculations in January 1999 at your request. <br /> The mass balance calculations were based on empirical data derived from previous site activities as <br /> well as published literature of various soil properties. As such, the mass balance calculations should <br /> be construed to reflect approximate location and time-dependent contaminant quantities. They are <br /> best used comparatively to make general assessments regarding relative contaminant reduction and/or <br /> degradation, and should not be construed as defining actual mass quantities. <br /> Stepwise, the mass balance calculations were derived as follows: <br /> A) Two excavations were apparently performed at the site. According to data provided by your <br /> office, the excavation dimensions were as follows: <br /> Excavation 1) A larger northern excavation, measuring approximately 24 feet by 15 <br /> feet by 11 feet deep. <br /> Excavation 2) A smaller southern excavation, measuring approximately 17 feet by 9 <br /> feet by 12 feet deep. <br /> B) The above dimensions equate to soil volumes of 3,960 cubic feet (ft3) and 1,836 ft3, <br /> respectively. <br /> C) Given that laboratory contaminant concentrations are expressed as a ratio of contaminant <br /> mass to soil mass, the above soil volumes need to be converted to mass equivalents. This is <br /> accomplished by applying a soil density factor. <br /> Rancho Cordova South Lake Tahoe Atascadero <br /> 11350 Monier Park Place, Rancho Cordova, CA 95742 Tel: 916.853.8025 Fax: 916.853.8029 <br />