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The Mean Time to Corrosion Failure (MTCF) for 'this tack cluster was calculated to be 14.9 years. C ontributdng to the corrosion rate are high soil maL t ure contents and high soil conductivity. 3.4 Pdcrity Index The priority index (PD is cake ated by subtracting the M T C F from the age of the tacks at the site. Since all tanks were histalled in 1983, the priority index is -1().9. These induces are then usually grouped in three general categories arranged according to Probable Leakage, High PI and Low PI. Extremes in the best results and locations of potable water supplies are also qualitatively assessed by the corrosion engineer, which can result in a particular site to be moved up from the Low PI to High PI category. This tank cluster falls in the Low PI category with resect to a large national data base. 4.0 RECOMMENDATIONS FOR IAP Not withstanding the pending Federal, State and Local regulations regarding underground tanks, the development of a comprehensive Integrity Assurance Program (IAP) requires an evaluation of both safety and economic considerations. Each of the three general categories should be approached differently as discussed below. Note that within each category, pr=ities can be estahlished in accordance with the PL For your reference, the f Dowing di.cussion is also summarized on the ZAP Decision Flow Diagram in Appendix C. In all cases, good planning will save you considerable monies in the construction phase of the project through proper stages and coordination. 4.1 Probable I eta If leakage were probable, the presence of an existing leak should be confirmed, and appropriate steps taken to evaluate the degree of contamination and clean-up requirements. A busing decision then needs to be made whether to repair, replace or abandon the tank. if repairs are made, the tank should be retrofitted with external cathodic: protection. Internal ccrrosion protection can also be considered at that