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Report:Groundwater-quality Monitoring—March 29-31,2006, 7500 West Eleventh Street, Tracy, C4 Page 29 4.� Di-isopropyl ether EPA Method 8260B 4,.. Ethyl tertiary-butyl ether EPA Method 8260B ' Tertiary-amyl methyl ether EPA Method 8260B r. In addition to the annual scope of groundwater-quality monitoring described above, in * compliance with the results of the MAROS monitoring-program optimization analysis, if a greatly-extended period of monitoring should be necessary following the July 2007 annual round of groundwater-quality monitoring, samples should be recovered from all + 24 wells in the shallow aquifer at the site on a biennial schedule, beginning with the July �,. 2008 sampling round. y 8,2 Closure of Redundant Wells Monitoring Wells MW-3A, MW-3B and MW-12A have had no useful function since they were installed in April 2002 (The San Joaquin Company Inc. 2002c) and recovery of �- groundwater samples from them confirmed the findings that had previously been developed from the stratigraphic studies, site-wide groundwater-quality monitoring program and analysis soil samples recovered from an extensive array of push probe �- borings drilled at the site in April 2000 that included recovery of samples from deep beneath the shallow aquifer (The San Joaquin Company Inc. 2001d), that aquifers deeper * 1 than the shallow aquifer are unaffected by components of fuel hydrocarbons. SJC is concerned that the continued existence of the wells that penetrate into the pristine deep aquifers beneath the site poses an unnecessary risk to groundwater quality, situated ' as they are in a yard that is frequently occupied by heavy trucks and where diesel may spill from truck tanks. This concern is not merely speculative. On August 3, 1999, a tractor-trailer rig stopped at the Casa Mendoza restaurant at 7500 West Eleventh Street and ruptured its fuel tank. Some 150 gallons of diesel spilled onto the ground surface and penetrated into the soil of the unpaved lot. That incident required an emergency response by the SJCEHD and Dietz Irrigation to contain the spill and excavate affected soil to #` remediate the area (Dietz 1999, Sassoon 1999). We, therefore, again recommend that Monitoring Wells MW-3A, MW-3B and MW-12A be closed under the permit and oversight of the SJCEHD. 8.3 Monitoring and Management of Light Non-aqueous Phase Liquid A program designed to monitor the presence of LNAPL in monitoring wells MW-7, MW-14 and MWFP-I through MWFP-5 has been conducted at a quarterly frequency over the past two years. With the exception of Monitoring Well MW-7, no floating product has been detected in any of those wells and the concentrations of components of fuel hydrocarbons detected in samples of groundwater recovered from them have generally been orders of magnitude lower that their saturation concentrations. ` The groundwater in Monitoring Well MW-7 has been monitored for the presence of LNAPL since May 11, 2000. Over that period, small to moderate thicknesses of floating sic a