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Sent by: STRUCTURES LAB,CSULB 562 985 4406 06/09/99 12:08 Job 176 Page 2/2 of about 3 psi (about 8 hour period) on the annular space only. Determine whether or not water is still evident at the lowest point or at the location of the electronic sensor. If no water is present at the location of the electronic sensor, a standard vacuum test shall be conducted per recommendations of CS to certify the tank. If both the vacuum and the pressure test pass, then I believe the tank should be considered acceptable and certifiable_ If either the vacuum or pressure test fail in the last part of Step 2, then it is evident that the secondary wall is leaking water into the annular space. Based on past experience, it is my opinion that the location of this cracked secondary wall region is difficult to determine, even with the use of helium or other types of tracing; gases, especially when the concrete slab has been poured over the tank. If no other procedure is feasible in determining whether or not the secondary shell is leaking. I would then recommend that the tank be removed from the ground and the standard procedures recommended by CS be employed to determine the location of the leakage followed by repair. utilizing the procedures outlined by CS. To pressurize the annular region alone requires considerable care, to avoid damage to the tanks. It is, therefore, recommended to pressurize the primary tank, bleed into the annular region, then remove the pressure from the primary tank. While removing the pressure from the primary tank, the valve to the annular space should be closed. It is possible that the pressure in the annular space will drop significantly after the primary tank has been depressurized, due to the elastic deformations of the primary shell. Therefore, this process may have to be repeated several times, to attain a reasonable pressure of about 3 psi in the annular region only. The pressure in the primary tank should be the maximum nrescribed by CS for such a testinsr nrocedure.