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Ms. Carol Oz `f <br /> San Joaquin County <br /> Public Health Services <br /> August 25, 1989 <br /> 4. The Fire Permit will be obtained and submitted to your office prior to <br /> commencing this tank removal project. <br /> i <br /> 5. Detailed Description of Tank Purging Technique <br /> After the tank has been thoroughly cleaned, the tank will be purged with <br /> dry ice based on a minimum of 15 pounds of dry ice per 1000 gallons of tank <br /> capacity. <br /> The dry ice is used to displace hydrocarbon and oxygen vapors contained <br /> within the tank. Both types of vapors contribute to potentially explosive <br /> situations. <br /> The tank is monitored with a direct reading instrument which measures % LEL <br /> and % Oxygen concentrations. If the % LEL is above acceptable levels <br /> (generally 10 to 15 per cent), additional dry ice will be added. <br /> 6. Soil Sampling Sheet <br /> The San Joaquin Local Health District minimum verification lab analyses <br /> sheet has been completed and is attached. The analyses that will be <br /> performed are based on the type of material that is stored on the tank <br /> being removed. <br /> 7. Detailed Description of Tank Rinsing Technique <br /> DECON Environmental Services uses an approach for cleaning tanks that , <br /> facilitates the purging and removal operations. DECON first removes all of <br /> the remaining product from the tank. The second step is to excavate the <br /> top of the tank to provide ready access to the tank for cleaning. The tank <br /> is then cleaned using high pressure water combined with either hot water, <br /> steam, and/or degreaser or detergent, depending upon what was stored in the <br /> tank and the condition and age of the tank. Rinsate is pumped from the <br /> tank either by vacuum truck or into 55 gallon drums using an air-driven <br /> double diaphragm pump. The tank is then monitored for % LEL. <br /> This procedure is repeated until the % LEL in the tank has been reduced to <br /> around 10 per cent or less. The tank will be cleaned more than three <br /> times if the % LEL cannot be reduced to acceptable levels. <br /> 8. Detailed Description of Soil Sampling Technique <br /> After the tank has been removed, the backfill will be removed from the <br /> excavation. Soil samples will then be collected by excavating <br /> approximately 2 feet into the native soil and collecting a scoop of soil <br /> with the backhoe bucket. The soil sample will be collected by driving a <br /> clean brass tube into the soil at the base of the bucket closest to the <br /> teeth (this represents the soil at the bottom of the excavation) using hand <br /> pressure or a hammer. <br /> 2 <br />