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` Sent by: STRUCTURES LAB,CSULS 562 985 4406 03/26/99 13:37 Job 721 Page 213 MEMORANDUM I'0Rill Merchant ARCO t•ktfM. I.M. Plccnik Consultant 1R84 San Ansel ine Long Beach, CA 90815 (562)985-4406 1)ATI March 26. 1999 SUFUFC`I': Inspection of Two Underground Fib-erglass Tanks at the ARCO Cuts Station at the Intersection of freeway 99 and Route 124 in Manteca,Caliti)rnia On March 25, 1990, 1 inspected two fiberglass tanks, both 8 ft.dianrcter single wall tanks. manulactured by Owens Corning prior to 1985. The purpose for inspecting the tanks was to evaluate their structural integrity as well as any degradation of the interior surlace. The longitudinal axis of the two tanks are in the North/South direction. "therefore. the tanks referred to herein will he referred to as either the Last or the West tank. Fluid Containment repair crew also labeled these tanks as Tank No. I, which 1 would refer to as the West tank.and tank No. 2 us the last 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 7.ero. In the following, I will describe the results of my evaluation for each of the tanks individually. l;t)r the West tank,both Fluid Containment and 1 measured the internal diameters of the tank at six locations(Data provided to Mr. Wilson),from otic end of the tank to the other. These measurements were in the vertical,horizontal,and two diagonal directions. i herefore,a total of twemy-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 ('R 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 ofovalling hased on the original diameter of 92 in. is thus 11/16 in., which represents a relative det'o oration 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 42 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 Lank,but this is typical liar 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 laver or any extensive penetration of the gasoline into the laminate. In addition to visual inspection,the inner surface of the tank was ZO-d 0929 V139 916 '00 S-LonOOHd 03UV VV9=0T 66-8Z--AEW