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:Cvvz V( D A S S O C I A T E S I N C collected from MW3 have ranged from below laboratory detection limits to 150 ug/l MTBE has not been detected in MW3 during the two most recent groundwater monitoring ' events A hydrograph depicting TPHg concentrations associated with MW3 is shown on Figure 9 t • Groundwater samples have been collected from well MW4 and analyzed since January 1994 Well MW4 is located directly adjacent to the south of the former UST locations TPHg and BTEX concentrations in water samples collected from MW4 have shown a overall decreasing trend from concentrations of 170,000 ug/i (TPHg) and 45,000 ug/l (benzene) in January 1994 to concentrations of 330 ug/l (TPHg) and non-detect (benzene) ' during the fourth-quarter 2003 quarterly groundwater monitoring event conducted on November 28, 2003 The fourth-quarter 2003 TPHg and BTEX concentrations were the lowest since sampling began and represents a 99 8% reduction in TPHg concentration Additionally, the concentration of benzene was below laboratory detection limits While the groundwater was sampled for petroleum hydrocarbons since 1994, quarterly groundwater sampling for MTBE was not initiated until December 1997 MTBE ' concentrations detected in the groundwater samples collected from MW4 have ranged from 55 ug/l to below laboratory detection limits to 8 9 ug/1 A hydrograph depicting TPHg concentrations associated with MW4 is shown on Figure 10 • Groundwater samples have been collected from well MWS and analyzed since March ' 1996 Well MW5 is located approximately 110 feet to the west of the site, across Buena Vista Avenue, in a hydrologically downgradient direction TPHg and BTEX concentrations in water samples collected from MW5 have shown an overall decreasing trend from ' concentrations of 2,900 ug/l (TPHg) and 0 5 ug/l (benzene) in March 1996 to below detection limits during the fourth-quarter 2003 quarterly groundwater monitoring event conducted on November 28, 2003 While the groundwater was sampled for petroleum ' hydrocarbons since 1996, quarterly groundwater sampling for MTBE was not initiated until December 1997 MTBE was only detected in MW5 once, at a concentration of 160 ug/1 A hydrograph depicting TPHg concentrations associated with MW5 is shown on + ' Figure 11 • Groundwater samples have been collected from well MW6 and analyzed since April 1997 ' Well MW6 is located approximately 130 feet to the northwest of the site, across Monte Diablo Avenue and Buena Vista Avenue, in a hydrologically crossgradient to upgradient ' direction TPHg and BTEX compounds have never been detected in MW6, with the exception of one detection of xylenes in November 2000 Additionally, Oxygenates (including MTBE) have never been detected in MW6, with the exception of one detection 1 of DIPE in July 2000 i Groundwater samples have been collected from well MW7 and analyzed since April 1998 Well MW7 is located approximately 25 feet to the east of the site in a hydrologically w 1271421reponslclosure doc 15