ARCHIVED REPORTS_MONITORING WELL M-10 INVESTIGATION REPORT 2010

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M-10A Investigation Report November 30, 2010 Nestle USA, Inc., Ripon, California groundwater sample during the 2005 investigation was from an offsite location (CPT-4), west of Industrial Avenue (Geomatrix, 2006). • The distribution of TCE in the lower A zone appears to be continuous from the Site northwest to CPT-28, located approximately 200 feet downgradient of former MW-4. • TCE concentrations in the upper A zone and lower A zone extend farther to the northwest than the TCE concentration in the middle A zone. This TCE distribution suggests that pumping at MW-4, screened in the upper A and lower A zones (Section 2.2), has influenced the movement of TCE-affected groundwater in this area after pumping at MW-1, Regal Almond, and Nestle had ceased or become substantially reduced. Cross section B-B' (Figure 5) shows: • The highest concentrations of TCE near well M-10A, northwest of the Site, are located primarily in the upper A and lower A zones. The TCE concentrations reported for groundwater samples collected near well M-10A decrease from approximately 300 pg/L to 10 pg/L 350 feet to the west. Cross section C-C' (Figure 6) shows: • The highest TCE concentrations in the area immediately northwest of the Site were reported in groundwater samples from the lower A zone (960 pg/L) and middle A zone (590 pg/L). • The distribution of TCE in the upper A zone appears to be discontinuous between CPT-25 and CPT-23 to the west, suggesting that two separate plumes may exist, indicating a secondary source. Figure 7 (Upper A zone), Figure 8 (Middle A zone), and Figure 9 (Lower A zone) present the total VOC concentrations observed in CPT-1 through CPT-18 (drilled in 2005 on and around the Site and reported in Geomatrix, 2006), CPT-19 through CPT-32, and any wells which are screened in the zone represented on each figure, illustrated in a pie graph at each boring location. The pie charts represent the concentrations of TCE, cis- 1,2-DCE, and vinyl chloride as a percentage of the total COC concentration. These figures show: • Concentrations of TCE are present in the upper A zone. Little or no cis-1,2-DCE and vinyl chloride are observed in the upper A zone. • The middle A zone COC distribution is similar to the upper A zone COC distribution, except to the southwest of the Site near historical CPT borings CPT- 6, CPT-7, and CPT-8. These borings contain a higher relative percentage of cis- 1,2-DCE. • Offsite borings in the lower A zone also consist primarily of TCE concentrations, with the exception of CPT-30, located on the west side of the B-B' cross section, which contains a higher relative percentage of cis-1,2-DCE. The graphical interpretation of historical pumping presented on Figure 10 shows: • The pumping from on-site wells EI-1 and EW-1 was variable during the time period from 1999 to 2008: 9