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 4.2.1 UPPER A ZONE TCE RESULTS (50 TO 80 FEET BGS) The 2010 CPT analytical results for the Upper A zone indicate the highest TCE concentrations offsite were located immediately adjacent to and cross-gradient of monitoring well M-10A in CPT-19 through CPT-22 (Figure 4). Concentrations of TCE in these borings ranged from 140 pg/L in CPT-22 to 280 pg/L in CPT-20 on (Figure 7). The lowest TCE concentration was observed in CPT-32 at 3.9 pg/L (near location of municipal well MW-4). 4.2.2 MIDDLE A ZONE TCE RESULTS (80 TO 95 FEET BGS) The results for the Middle A zone (Figure 8) indicate that the highest concentrations of TCE were hydraulically upgradient (southeast) of well M-10A, in CPT-24 (580 pg/L), CPT-25 (590 pg/L), and CPT-26 (470 pg/L). The next highest concentration was observed downgradient of these wells in CPT-20, located adjacent to M-1 OA (120 pg/L). 4.2.3 LOWER A ZONE TCE RESULTS (100 TO 115 FEET BGS) For the lower A zone, the highest TCE concentration was reported in in CPT-25 (960 pg/L), and TCE was detected at multiple locations (CPT-19, CPT-20, CPT-21, CPT-24, CPT-27, and CPT-32) downgradient of CPT-25 with concentrations of TCE ranging from 84 pg/L (CPT-32) to 330 pg/L (CPT-20). The groundwater samples from CPT-30 and CPT-23 were reported to contain cis-1,2-dichlroethene (cis-1,2-DCE; at concentrations of 5.9 and 4.5 pg/L, respectively) (Figure 9). 4.2.4 OTHER CHEMICALS OF CONCERN Tetrachloroethene (PCE), a non-Nestle-related COC, was observed in CPT-20, CPT-24, CPT-25, and CPT-28. All detections of PCE were only slightly above the laboratory reporting limit (RL: 0.5 pg/L) except in CPT-28 at a concentration of 21 pg/L. CPT-28 is located farthest downgradient from the Site (Figure 2). The source of the PCE is unknown and is not associated with activities at the Site. Concentrations of 1,1-dichloroethane (1,1-DCA) were observed slightly above RLs in CPT-24 and CPT-25. Concentrations of 1,2-dichloroethane (1,2-DCA) were observed in CPT-24 through CPT- 27. The concentrations ranged from 0.64 pg/L (CPT-27) to 9.9 pg/L (CPT-24). The source of the 1,2-DCA observed in these samples is likely from another urban source, as the historical use of 1,2-DCA has not been reported as part of the former Nestle operations and because 1,2-DCA was not reported in groundwater samples collected on Site. A likely source of 1,2-DCA is historical releases of leaded gasoline from underground storage tanks that were located at gasoline service stations. 1,2-DCA was used as an anti-knock agent in leaded gasoline formulations. Chloroform was observed in CPT-24, CPT-25, CPT-26, and CPT-31 at concentrations ranging from 20 pg/L (CPT-31, 102 feet bgs)to 1.8 pg/L (CPT-25, 88 feet bgs). 5 DISCUSSION Nestle has completed multiple investigations at the Site, offsite at 519 South Stockton Avenue, and in areas surrounding both location s',8,9,10,11. These investigations indicated potential COC sources offsite near the Regal Almond and Ripon Milling 12, 13 facilities and 7