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v o � A S S o c I A T E 3 I N C Groundwater samples collected from MW 1 and MW7 contained slightly increased concentrations of TPHg and BTEX with respect to the samples collected from these wells in March 2003 There are petroleum hydrocarbons remaining in the soil and groundwater The direction of groundwater flow and the magnitude of hydraulic gradient are generally consistent with the previous event Groundwater elevations have increased slightly since March 2003 The vapor extraction system is operating at approximately 70 cfm and petroleum hydrocarbon vapor concentrations in vapor wells V W 1 and V W2 decreased during the second quarter with respect to the first quarter 2003 Petroleum hydrocarbon vapor concentrations in vapor wells VW3 and VW4 decreased during the second quarter with respect to the fourth quarter 2002 when operation of the system was initiated The vapor extraction system is extracting approximately 31 gallons per hour from vapor wells V W 1, V W2, VW3, and VW4 The air sparge system appears to be operating within design parameters RECOMMENDATIONS Based on the results of the Second Quarter 2003 monitoring event, we recommend the following • Conduct the Third Quarter 2003 groundwater monitoring and sampling of wells MWI through MW 10 and CW and analyze samples for TPHg and BTEX by EPA methods 8015B and 8021B, respectively, and MTBE, ETBE, TBA, TAME, and DIPE by EPA method 8260B • Continue monthly monitoring of the vapor extraction, groundwater treatment and discharge system, and air sparge system Please contact our office at (209) 579-2221 if you have any questions or comments Respectfully submitted, ATC Associates Inc Todd Hafner Project Geologist F ".. Drew Van Allen Senior Project Manager x3 ; J anne Homsey, P E �J'"- P +� CA Registered Civil Engineer No 47410 .,;, cc Mr and Mrs Raymond Farmer Jim Barton, RWQCB w 4ordpro1625961quart1yl2gr-2003 doc 8