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First Quarter 1996 Status Report - Unocal Station No 116981 April 25, 1996 thermal mode from startup in September 1994 until January 1995, when it was shut down and switched to catalytic mode The system was restarted in catalyic mode on May 16, 1995, but could not meet permit discharge conditions and was shut down on May 23, 1995 to evaluate the catalyst A new catalysit was installed and the system restarted on �-- December 19, 1995. Historical VES chemical analytical data are summarized in Table 1, and historical VES operational data are summarized in Table 2 CURRENT QUARTER'S ACTIVITIES Field activities conducted at the subject site during the first quarter 1996 are discussed below Monitor= and Sampling of Groundwater Monitoring Wells i Groundwater monitoring wells were monitored and sampled by MPDS Services, Inc of Concord, California on January 24 and 25, 1996 Based on measurements collected by MPDS, the groundwater beneath the site appears to flow to the northeast at an approximate gradient of 0 004 (consistent with previous data) The groundwater table was approximately 2 8 feet higher than the previous quarter All groundwater monitoring wells at the site (MW-1 through MW-13) are sampled on a semi-annual basis, during the first and third quarters Only the perimeter wells MW-6 and MW-9 through MW-13 are sampled on a quarterly basis During the first quarter 1996, Total Petroleum Hydrocarbons as gasoline (TPHg) were detected in groundwater samples from wells MW-2 (2,100 parts per billion, or ppb), MW-5 (86 ppb), and MW-7 (76 ppb) Benzene was detected in the groundwater samples form wells MW-2, MW-4, MW-5, and MW-7 at concentrations ranging from 1 4 to 510 ppb Methyl Tertiary Butyl Ether (MTBE) was identified in groundwater samples from wells MW-1, MW-2, MW-4, and MW-5 at concentrations equal to or above the taste and odor threshold of 40 ppb The Quarterly Data Report dated February 15, 1996 was submitted by MPDS to the San Joaquin County Public Health Services (SJCPHS) and California Regional Water Quality Control Board (CRWQCB) VES Operation The VES effluent vapor stream was sampled by Gettler-Ryan Inc of Dublin, California (G-R) on January 24, February 26, and March 26, 1996 The samples were analyzed for TPHg and BTEX at Sequoia Analytical (Sequoia) in Redwood City, California (FLAP 4855 02-7 2