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t® rYMPANIESORRPRO INC July 6, 2001 For Every Corner of Your World CCI 9575-2252 2799 Miller Street San Leandro,CA 94577 'rel: 5101614-8800 • Fax: 510/614-8811 Carpenter Company, Inc. E-mail:sanleandro@corrpro.com P. O. Box 279 17100 South Harlan Road - -- - ----- _ - - Lathrop' CA 95330 ; '�' Attention: Mr. Ed Ware (Maintenance Manager) �. AUG .. 6 2001 I; Subject: Underground Diesel Storage Tank :_ Cathodic Protection System Survey at Carpenter Co. Lathrop, CA Division Gentlemen: Corrpro Companies, Inc. performed a cathodic protection survey on the 10,000-gallon capacity, underground diesel fuel storage tank (UST) at the subject facility on June 27, 2001. The purpose of the survey was to evaluate the performance of the existing cathodic protection (CP) system and to make any necessary recommendations for remedial actions to comply with EPA 1998 external corrosion control requirements. The structure under consideration at the subject site consists of a double-wall, steel underground storage tank (UST). The tank was originally constructed to meet STIP-3 requirements, with directly connected magnesium or zinc galvanic anodes. All piping, risers fuel dispenser and conduits were either electrically isolated from the tank at the time of the UST installation or were of non-metallic construction. A structure-to-soil potential survey was completed at the facility. Structure-to-soil potentials were measured using the DC voltmeter circuit of a high-impedance digital multimeter and a portable copper-copper sulfate reference electrode. Structure-to-soil potentials were recorded for the tank and for the associated risers to confirm the correct operation of the cathodic protection systems. Electrical connection to the tank was made using a probe inserted inside the tank (stabbing the tank bottom) as no test lead were found at any of the tank risers. The survey can only record "anode connected" potentials as the anodes are directly connected to the tanks below grade. The recorded data is presented in Appendix 1 of this report. The recorded structure-to-soil potentials for the tank indicates the following: • The diesel tank is cathodically protected in accordance with NACE R1,30285-95 -850 mV criteria, and therefore satisfies the EPA 1998 requirements for external corrosion control (See Appendix 2). • The risers and associated conduits are electrically isolated from the tank.