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v TC � A S S O C I A T E S I iN C details and VET test methodologies, as well as additional tasks such as a groundwater receptor survey ATC agreed to contact the Fund to discuss additional pre-approval requirements It is not anticipated the change of scope will exceed the amount previously pre-approved by the Fund on November 1997 QUARTERLY MONITORING ACTIVITIES ATC performed quarterly groundwater monitoring and sampling on October 7, 1999 Field work included measuring the depth-to-water in wells MW1 through MW6 and purging and sampling the water from wells MW1, MW2, MW3, MW4, MW5, and MW6 in addition to the nearby Thornton No 2 Municipal Supply Well (Supply Well) The samples were analyzed for the presence of dissolved petroleum hydrocarbons Depth to water measurements were collected on October 7, 1999 from monitoring wells MW1 through MW6 The water table elevation has decreased an average of 1 82 feet in the monitoring wells since the last monitoring event in July 1999 The October 1999 groundwater measurements indicate the water table is at the lowest level since September 1994 Groundwater beneath the site generally flows in a westerly direction at an average gradient 0 0007 ft/ft, or approximately 4 foot/mile, with apparent mounding in vicinity of MW3 Historically, groundwater beneath the site generally flows in a westerly direction Groundwater monitoring data are summarized in Table 1 A groundwater gradient map for the October 1999 monitoring episode is shown on Figure 2 Groundwater samples were collected from wells MW 1 through MW6 after purging and stabilization of physical parameters (pH, electrical conductivity, and temperature) The monitoring wells were purged and sampled according to ATC's Field Procedures on file with PHS/EHD Monitoring well purge logs are included in Attachment 1 Furthermore, ATC and coordinated with San Joaquin County Utility Maintenance Division personnel and collected a water sample from the sampling port of the Supply Well Collected groundwater samples were placed on ice and transported under chain-of-custody to State-certified Sequoia Analytical laboratory (ELAP #1210) Samples were analyzed for benzene, toluene, ethylbenzene, and xylenes (BTEX) by EPA method 8020, and TPHg by EPA method modified 8015 RESULTS Laboratory analyses detected petroleum hydrocarbon constituents in the sample collected from well MW4 The constituent concentrations detected include TPHg (2,700 parts per billion [ppb]), benzene (11 1 ppb), toluene (11 3 ppb), ethylbenzne (57 5 ppb), and xylenes (64 6 ppb) W 1625821quartlyl3gr-1999 doc 4