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v o • A S S O C I A T E 5 1 N C Groundwater Flow Direction Water level measurements were collected from MW1 through MWIO, VW1, VW2, and CW on June 8, 2004 Water levels ranged from 24 83 to 28 58 feet below the tops of the well casing elevations, representing an average decrease in the water table elevation of approximately 0 21 Lfeet since March 2004 The water level data were used to develop a groundwater elevation contour map (Figure 3) Assuming that horizontal isotropic conditions prevail, shallow groundwater beneath the site flowed toward the northeast The average hydraulic gradient on June 8, 2004 was calculated to be 0 009 ft/ft or approximately 48 ft/mile A summary of groundwater monitoring data is presented in Table 1 ' REMEDIATION SYSTEM MONITORING ACTIVITIES 1 Vapor Extraction System Monitoring The installation and startup of the vapor extraction system located at the site is detailed in ATC's 1 Remediation System Installation Report for the Farmer Property, 610 North Hunter Street, Stockton, California, dated April 8, 2003 After the modifications described in the Remediation System Installation Report were made to the system, ATC started the vapor extraction system on December 19, 2002 During the current reporting period, ATC personnel monitored the vapor extraction system on April 26, May 26, and June 28, 2004 Parameters monitored in the field included vapor extraction flow rates, hydrocarbon vapor concentrations, groundwater extraction rate, total groundwater discharged to the City of Stockton sanitary sewer, and total hours of system. operation Field monitoring data are contained in Attachment 3 On April 26 and June 28, 2004, ATC personnel collected vapor samples from wells VW1, VW2, V W4, MW 1, and from the influent and effluent vapor streams of the vapor extraction system The samples were transported under chain-of-custody documentation to SunStar Laboratories, Inc (ELAP #2250) in Tustin, California and were analyzed for VOCs by EPA method TO-14 ' On April 26 and June 28 2004 ATC personnel collected water samples from the groundwater p p P treatment and discharge component of the vapor extraction system Water samples were collected ' from the influent, effluent, and vessel I of the groundwater treatment system and transported under chain-of-custody documentation to Argon Labs for analyses The water samples were analyzed for TPHg by EPA Method 8015B, BTEX by EPA Method 8021B, and MTBE, TAME, ETBE, DIPE, TBA, 1,2-DCA, and EDB by EPA Method 8260B On May 26, 2004, the groundwater treatment and discharge component of the vapor extraction system was down,consequently groundwater samples were not collected ie s\enviro1625961quar[1y12gr-2004 doc 4 1