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sud Mr. Harlin Knoll,SJCEHD June 18,2007 Well installation Work Plan A. Teichert and Sons Property, Stockton,CA Page 5 During the January 2006 CPT investigation, GRO was reported only in boring CPT-2 at 73 feet bgs (51 µg/L) and 126 feet bgs (180 µg/L). GRO concentrations in samples collected at 83, 95, and 112 feet bgs in boring CPT-2 were below laboratory reporting limits, and GRO was not reported in any of the samples from the other CPT borings. Benzene and MTBE were not reported in any of the CPT samples. Based on these data and data from the former monitoring well network, the lateral extent of GRO and MTBE impact appears to be limited to the area in the immediate vicinity of wells MW-13, MW-14, and boring CPT-2. Benzene has historically been reported in these wells, but concentrations have shown a decreasing trend, and benzene is at very low or non-detectable concentrations in recent samples (Figure 6). The CPT data collected in January 2006 suggests that the vertical extent of GRO, benzene, and MTBE impact has been adequately characterized. Additional characterization of the GRO, benzene, and MTBE plumes does not appear warranted. During the January 2006 CPT investigation, 1,2-DCA was reported in samples collected from borings CPT-2 (73 and 83 feet bgs), CPT-3 (71 and 80 feet bgs), CPT-4 (77 and 97 feet bgs), CPT-5 (71 feet bgs), and CPT-8 (62, 72, and 81 feet bgs). The highest 1,2-DCA concentration (140 µg/L) was reported for the sample collected at 72 feet bgs in boring CPT-8. 1,2-DCA was reported in samples collected at each of the CPT boring locations in October 2006. Concentrations of 1,2-DCA were reported at 62 µglL (63 feet bgs) and 27 µglL (72 feet bgs) at boring CPT-10, located east-northeast of boring CPT-8. The highest concentration of 1,2-DCA reported during this phase of investigation was observed at off-site boring CPT-13 at 72 feet bgs (99 pg/L). 1,2-DCA impact appears to be predominately situated above approximately 90 feet bgs. However, 1,2-DCA has been reported in two groundwater samples collected below 90 feet bgs (boring CPT-4 at 97 feet bgs [5.9 l.tg/L] and boring CPT-11 at 109 feet bgs [4-5 µg/L]). Remedial Actions Soil Overexcavation Following removal of USTs A, B, and C by Triangle, LBME excavated petroleum hydrocarbon impacted soil from the area north of the warehouse and lubrication station between September 15 and 18, 1987. The excavation measured approximately 47 feet in length by 25 feet in width at the ground surface. The sides of the excavation were terraced, and the excavation narrowed with depth. The deepest portion of the excavation was approximately 38 feet bgs. Approximately 1,700 cubic yards of soil were excavated and aerated prior to disposal. K:7eichertlStockton-103Mork Planslteichert-well install work plan 06-2007.doc SmAlus