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 ■ Nestle conducted a permanganate pilot study between August 1999 and August 2000 during which no on-site wells were pumping. ■ From August 2000 to April 2005, only well EW-1 was pumping and the graph indicates a gradual drop in the pumping rate during this period. ■ Well EI-1 was pumped at approximately 160 gpm for one month between April and May 2005 while EW-1 continued to pump at a declining rate. ■ In August 2006, pumping began at well EW-1 at rates between 160 gpm and 120 gpm until February 2008 when pumping at wells EW-1 and EI-1 was stopped to implement the Interim Remedial Action Plan. ■ In June 2003, the pumping rate at well EW-1 fell below 30 gpm and continued to decline. ■ In August 2006, well EI-1 began pumping at approximately 160 gpm and continued to pump until both wells EW-1 and EI-1 were shut down in February of 2008. • In July 2004, approximately 400 days after the pumping rate in well EW-1 fell below 30 gpm, the TCE concentrations in well M-1 OA began to increase. • The TCE concentration in well M-10A dropped in April 2006, approximately 400 days after well EI-1 pumped at 160 gpm for a month, but subsequently began to increase when well EI-1 was shut down and EW-1 was pumped at approximately 15 gpm. • In October 2007, approximately 400 days after pumping was re-started at well EI- 1, the TCE concentrations in well M-10A decreased again. • The concentration of TCE in well M-10A did not increase again until July 2009, approximately 500 days after wells EW-1 and EI-1 stopped pumping. • There is an inverse correlation between pumping at wells EW-1 and EI-1 in the lower A zone at the Site and concentrations of TCE in well M-1 OA. • The "lag time" for the pumping signal to arrive at well M-1 OA is between 400 and 500 days. 5.2 CONCLUSIONS AND RECOMMENDATIONS ECM's conclusions are based on (1) analysis of Iithological information and hydropunch sample results obtained from CPT investigations, (2) analysis of historical operation of extraction wells, (3) evaluation of historical operation of municipal supply wells, and (4) spatial and temporal analysis of concentration of COC in wells in the vicinity of well M- 10A described above. ECM concludes the following related to how the operation of the on-site extraction wells and municipal supply wells could have influenced the movement of COC: • Data suggests that a decline in A-zone on-site groundwater extraction (extraction by EI-1 and EW-1) and the influence of changes in the pumping schedule at well MW-4 may have caused concentration increase in M-10A; • Groundwater samples from the Site and the area north and west of the Site have been shown to contain COC concentrations that appear to be related to the 10