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Ir Miftelhauser C 0 R P 0 R A r 1 0 N 7901 Stoneridge Drive,Suite 123 Pleasanton,California 94588 (510)416-2900 Fax(510)416-0957 I..r April 15, 1993 Mr. Edward Ralston Unocal Corporation 2000 Crow Canyon Place, Suite 400 i■ San Ramon, California 94583 SUBJECT: Monitoring and Sampling Report First Quarter 1993 Unocal Service Station #6348 3788 Tracy Boulevard Tracy, California �- Dear Mr. Ralston: On March 17, 1993 Mittelhauser Corporation (Mittelhauser) monitored and sampled groundwater monitoring wells MW-1, MW-2, and MW-4 at Unocal Corporation's (Unocal) Service Station #6348 in Tracy, California. Monitoring well MW-3 had been abandoned on November 24, 1992 as part of the demolition and remediation activities `■ at the site. A new monitoring well will be installed at the site to replace MW-3 once the demolition work is complete. Water-level measurements indicated that the average depth to groundwater was approximately 8.0 feet on March 18, 1993 (see Table 1 ). The groundwater gradient was directed towards northwest at a magnitude of 0.0033 foot per foot (see the Groundwater Gradient Map, Figure 2). The groundwater samples obtained from wells MW-1, MW-2, and MW-4 on March w. 17, 1993 were submitted to ChromaLab, Inc., a state-certified laboratory in San Ramon, California with proper Chain-of-Custody documentation. The samples were analyzed for total petroleum hydrocarbons as gasoline (TPH-G), and benzene, toluene, ethylbenzene, and xylenes (BTEX). The field notes and monitoring and sampling protocol are attached to this report. Upgradient monitoring well MW-1 had been removed from the sampling program with approval of the San Joaquin County Department of Public Health Services. However, well MW-1 was sampled in the first quarter of 1993 pending the replacement of well MW-3. x w.� Your Partner in Environmental Management Chicago, IL Indianapolis, IN ■ Laguna Hills, CA ■ Pleasanton, CA