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. 1 i Mr. Harlin Knoll,SJCEHD -September 9,2009 Addendum to SCM and Environmental Case Closure Request Project No. 2001-0103-07 A.Teichert and Sons,Inc.Property,Stockton,CA Page 2 WATER QUALITY PROJECTIONS The Highest historical concentrations of GRO are consistently reported in well MW-13, which is situated near the former .UST storage area at the subject site (see Figure 2). Figure 3 depicts historical groundwater analytical data for GRO at well MW-3, available for samples collected between the third quarter 1992 and the second quarter 2009. Using this data, Stratus has included a linear regression trend line that projects future GRO concentrations at well MW-.13, fitted by the software used.to prepare the figure. Based on the historical GRO data trends at well MW-13, approximately 5 years appear necessary for GRO concentrations to reach water quality objectives-(for the purposes of this estimate, assume 100 micrograms per liter. [l.tg/L], based on correspondence with SJCEHD). The highest historical concentrations of 1,2-DCA are consistently reported for samples collected from well MW-17. Figure 4 depicts historical groundwater'analytical data for j 1,2-DCA at well MW-17, available for samples collected between the fourth quarter 2007 and second quarter 2009. Using this data, Stratus has included a linear regression trend . line that projects fixture 1,2-DCA concentrations at well MW-17, fitted by the software used to prepare the figure. Using the historical I,2-DCA data trends at well MW-17, approximately 13 years appear necessary for 1,2-DCA concentrations to decline to water quality objectives at the subject site (for the purposes of this estimate, assume current- California Primacy Maximum Contaminant Level of 0.5 µg/L, based on correspondence with SJCEHD). UNDERGROUND STORAGE TANK INFORMATION The following information summarizes available information regarding UST use at the site. Approximate locations of the USTs, and a summary table with information regarding these USTs, are included on Figure 2. All USTs and associated piping have been removed from the subject site. • In October 1986, two 5,000-gallon'gasoline USTs (designated as tanks A.and B) and one 1,000-gallon waste oil UST (designated as tank C) were removed from the subject site. • One 10,000-gallon gasoline UST (designated as tank D) was removed from the site in June 1988. • One 12,000-gallon double-walled diesel UST (designated at T-8) and one double- wailed waste oil UST(designated as T-4) were installed in August 1988. • Two 20,000-gallon diesel USTs (designated as T-5 'and T-6), and tank T-8, were removed in Match and April 1999. • Tank T-4 was removed in October 2000. K:41'eicicrtl5tockton-103U2cports\Ecichert- ddcndu melosure 08-26-09.doc STRATUS 1 1 i