SITE INFORMATION AND CORRESPONDENCE

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Stockton Avenue Groundwat TExtraction System Shutdown Request • November 5, 2009 to 158 feet bgs, was installed. Nestle began to extract groundwater from this well in mid- 2004. The extracted groundwater from well E-6 is treated with an air stripper because TCE breakdown products were present. Vapors from the air-stripper are captured and a catalytic oxidizer destroys COCs prior to release to the atmosphere. The treated water is discharged to the City of Ripon non-potable water system (NPS) for beneficial use. The initial design capacity of the Stockton Avenue System allowed for extraction and treatment of a combined flow from E-2 and E-6 of up to 500 gallons per minute (gpm). From 1999 through 2003, well E-2 operated at extraction rates in the range of 100 to 110 gpm. Extraction rates for well E-6 ranged from 350 to 450 gpm between 2004 and 2007. Beginning in the second quarter of 2007, the maximum sustainable pumping rate at well E-6 began to decline. Drawdown within well E-6 increased from initial levels of 60 feet, to over 120 feet. The well yield decreased from 430 gpm in March 2007 to 285 gpm in December 2007. Analysis of extraction rate and water level data (2007-2008) suggested a significant drop in well efficiency at well E-6. In response, ECM attempted to rehabilitate the well using a combination of surging and bailing and chemical methods during the week of June 23, 2008. Following these activities, sustainable pumping rates at well E-6 did not change significantly. VOC mass removal rates from wells E-2 and E-6 combined have declined from approximately 0.79 VOC lbs per day (during first quarter 2007) to 0.04 VOC lbs per day (during second quarter 2009). DISTRIBUTION OF COCS Historical concentrations of TCE and cis-1,2-DCE in the Upper and Intermediate Aquifers are illustrated in Figures 2 through 5. The source of COCs in the Upper Aquifer near the Stockton Avenue System is likely to have been associated with historical leaks from an industrial sewer line. The source of COCs in the Intermediate Aquifer is likely infiltration from the City wastewater treatment lagoons. Table 1 provides analytical data for monitoring wells in the area of the Stockton Avenue System. These data show an overall decreasing trend in COC concentrations at monitoring wells near the Stockton Avenue System (see Figures 2 through 5). In the second quarter of 2009, the Stockton Avenue System removed approximately 27.48 million gallons of water and 13.28 pounds of CDCs. This is equivalent to a VOC removal rate of 0.48 pounds of VOC removed per million gallons of water pumped and treated. The removal rate has decreased steadily from the second quarter of 2008, when 0.70 pounds of VOC were removed per million gallons of water pumped. The decrease is even more evident with a comparison to 2004 data, where 0.89 pounds of VOC were removed per million gallons of water pumped. The decrease in mass removal rate can mostly likely be attributed to two causes. The first cause is that TCE concentrations have steadily decreased in well E-2 to below 10 micrograms per liter (ug/L) since April 2007 (see Table 1). In addition, the COC mass removal from the Intermediate Aquifer (E-6) is extremely low, and the decline in the removal rate since 2007 has been correlated to the decrease in concentrations of COCs in the groundwater in the vicinity of E-6. Other area wells which are used to monitor the Upper Aquifer in the area of the Stockton Avenue System include M-8A, M-813, M-9A, and M-913. Figure 2 presents the TCE concentrations in wells M-8A, M-86, M-9A, and M-913 over time, with the influence of 2