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Sent by: STRUCTURES LAB,CSULB 562 985 4406 06109199 12:12 MEMORANDUM Job 177 Page 213 Ti) ('.L. Bryant FROM: J.M. Plecnik r � Consultant - " Z . 1880 San Anseline Long Beach. CA 90815 (562) 985-4406 DA FE.._ .lune 7, 1999 S1 WECT: Proposed Evaluation of 15,000 Gallon Containment Solutions UGT at Tracy, California (Tank with Inner Raffle) Based on discussions with various individuals, it would appear that the following Procedure would be most expedient in terms of evaluating the causes for water in the annular space for this double wall tank. Perform a visual inspection of the inner surface of the primary shell_ It is possible that if the exterior shell had been damaged (such as a blow), that minute cracks could appear on the inner surface of the primary tank without losing vacuum through the primary tank. That is, the minute crack structure on the inner surface could exist without any cracking on the exterior surface of the primary tank. If such a damaged region is evident on the primary tank, a cutout would be taken from the primary tank to expose the secondary tank. If the secondary tank is damaged in this region, a procedure for repair would be recommended with the approval of Containment Solutions (CS), which would also be acceptable to the county. It is very unlikely that the inner surface of the primary tank~ would show a crack pattern without any damage to the secondary tattle, If the visual inspection in Step 1 shows no damage or cracking on the inner surface of the primary shell, the next step will be to determine whether or not the secondary shell has a crack pattern which would cause leakage of underground water into the annular space. it is possible that the current water being removed from the annular space continues to trickle from the trapped regions of the annular space due to the presence of a thin plastic film which is used to separate the inner and the outer wall. A vacuum test on the annular space will tend to compress the two walls of the tank. closer together and not facilitate the release of the water from these entrapped regions. I propose that a small pressure (about 3 psi) be applied in the annular space only, to separate the primary tank from the secondary tank and facilitate the movement of the water in the annular space down to the lowest points. After this pressure has been applied for a period of 24 hours, drill three or four holes (about 1/2 in. diameter) in the primary tank wall at the location of the ribs to accelerate the removal of all the water from the annular space. Allow approximately 24 hours for the water to drain through these 1/2 in. holes. Upon completion of this time period, repair these 1/2 in. diameter holes according to CS procedure and apply pressure