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B. Secondary Containment (40 CFR 112.7(c)) Spill containment and diversionary structures for specific oil storage containers are as follows: • Outdoor Storage Area: AST No. 1 (10,000-gallon diesel tank) and AST No. 2 (1,000-gallon waste oil tank) are located within a concrete-walled area along the western border of the site. Based on the dimensions of the secondary containment structure (47 feet by 20 feet by 3.5 feet in height), the total volume of the exterior containment area is approximately 24,600 gallons. The top of the waste oil tank is just slightly above the top of the containment wall, and this tank decreases the containment capacity available to the largest tank in the containment system (i.e., the diesel tank)by approximately 1,000 gallons (to 23,600 gallons). Based on discussions with the Department of Water Resources', the 25-year 24-hour rainfall event for the Stockton area is 2.46 inches. This rainfall event would result in approximately 1,400 gallons of rain water accumulating in the containment structure. Therefore, the available secondary containment capacity for the largest tank is 22,200 gallons, which is more than adequate to contain a release from the largest tank and accumulation from a 25-year 24-hour rainfall event. *TANK WAS TEMPORARILY REMOVED FROM SITE 2-12-20. PENDING ACQUISITION OF A NEW TANK REPLACEMENT* • Indoor Storaze Area—Engine Oil Tank and Gear Oil Drums: AST No. 3 (570-gallon engine oil tank) is stored in a metal catch pan located in the storage shed attached to the repair shop building. The metal catch is 10 feet by 64 inches by 35 inches in height, which yields a total containment volume of approximately 1,160 gallons. The containment volume available to the tank is reduced by volume occupied by three gear oil drums located within the metal catch pan. The excluded volume is approximately 30 gallons each, based on 2-foot diameter drums, yielding a total available capacity of 1,050 gallons. The secondary containment capacity is thus adequate to contain the entire contents of the engine oil tank. • Indoor Storage Area—Transmission and Hydraulic Oil ASTs: AST No. 4 (600-gallon hydraulic oil tank) and AST No. 5 (275-gallon transmission oil tank) are stored in a metal catch pan located in the storage shed attached to the repair shop building. The metal catch is 10 feet by 64 inches by 35 inches in height, which yields a total containment volume of approximately 1,720 gallons. The containment volume available to the largest tank is reduced by 75 gallons by the portion of each of the two other tanks that are below the containment edge, and a 275 gallons by the portion of engine 'Personal Communication with Mr.William Mork of the State of California Department of Water Resources. Compilation of data from the Stockton Airport(1974 to 1997). -12-