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F i r MEMORANDUM S/0 TO: Bill Merchant P�F�F,y ARCO FROM: J.M. Plecnik w ` Consultant f No. 026354 1880 San Anseline Long Beach, CA 90815 Q, (562) 985-4406 T OF CAt\� DATE: March 26, 1999 SUBJECT: Inspection of Two Underground Fiberglass Tanks at the ARCO Gas Station at the Intersection of Freeway 99 and Route 120 in Manteca, California On March 25, 1999, I inspected two fiberglass tanks, both 8 ft. dieter single wall tanks, manufactured by Owens Corning prior to 1985. The purpose for inspecti g the tanks was to evaluate their structural integrity as well as any degradation of the interior surface. The longitudinal axis of the two tanks are in the North/South direction. Therefore, the tanks referred to herein will be referred to as either the East or the West tank. Fluid Containment repair crew also labeled these tanks as Tank No. 1, which I would refer to as the West tank, and Tank No. 2 as the East tank. Manways were installed on the northern end of the two tanks to allow for access. The tanks had been previously cleaned by Fluid Containment personnel. On the date of my inspection, the oxygen level within both tanks was approximately 20.9% and the LEL levels were near or at zero. In the following, I will describe the results of my a aluation for each of the tanks individually. For the West tank,both Fluid Containment and I measured the int rnal diameters of the tank at six locations (Data provided to Mr. Wilson), from one end of the tank to the other. These measurements were in the vertical, horizontal, and two diagonal directions. Therefore, a total of twenty-four diameter readings were obtained on each tank. The readings obtained by Fluid Containment personnel were nearly identical to mine with a variation of no more than 1/16 to 1/8 in. The most critical reading was at Location 5, which measured the vertical diameter of 91-5/8 in. and a diagonal diameter of 91-5/16 in. Since the diameter of the tank is 92 in. (probably plus or minus 1/16 in.) at the time of manufacturing, the largest amount of ovalling based on the original diameter of 92 in. is thus 11/16 in.,which represents a relative deformation of 0.75%, which is less than the 1% allowed by most specifications and Federal regulations. The other diameter readings were generally within 1/2 in. of the 92 in. original manufacturing diameter. Visual inspection of the tank interior surface indicated no chemical or mechanical degradation. No cracking was observed on either the shell or the domes. Discoloration of the resin is evident on the lower half of the tank, but this is typical for gasoline tanks of this age. Microscopic inspection was also performed at a number of locations. These indicted no degradation of the glass below the resin rich layer or any extensive penetration of the gasoline into the laminate. In addition to visual inspection, the inner surface of the tank was evaluated for